The present invention relates generally to an improvement in a pneumatic cylinder, and more particularly, to a pneumatic cylinder such as a cable cylinder, a rodless cylinder or the like having a mechanism for causing braking of the piston during operation.
Several types of power cylinders currently exist in the art including, among possible others, cable cylinders and rodless or band cylinders. Although the improvement of the present invention has application to all types of pneumatic cylinders including cable cylinders or band cylinders, it has particular application to rodless cylinders of the type generally described in U.S. Pat. No. 4,545,290. Such a rodless, pneumatic cylinder includes an elongated cylinder member, an elongated, longitudinally extending slot, a piston reciprocally movable within the cylinder member, a sealing means for successively sealing the slot during reciprocal movement of the piston and a piston bracket or other transfer means for transferring the reciprocal movement of the piston to a work piece or load outside of the cylinder. In one rodless cylinder for which the present invention has particular applicability, a piston bracket is connected to a carrier bracket of the type described U.S. Pat. No. 4,724,744 issued Feb. 16, 1988, the disclosure of which is incorporated herein by reference. In this structure the work piece or load is connected to the carrier bracket.
The carrier bracket of the above described structure includes a centrally located portion for connection with the piston bracket and a pair of spaced arms which extend outwardly from the central portion and partially around the body of the cylinder. The outer extremities of these arms carry a bearing rod or other means for sliding relationship with corresponding bearing channels or grooves in the side walls of the cylinder. During normal operation, the respective positions of these bearing rods are adjusted with sufficient clearance relative to the guide grooves to permit reciprocal movement of the carrier bracket and piston relative to the cylinder.
During the operation of such a cylinder, it is often desirable to stop the movement of the piston in the middle of a stroke. One way to do this, of course, would be to reduce or stop the supply of pneumatic power being supplied to drive the piston or to pressurize the opposite chamber so that the pressure in the respective chambers is equalized. While this will result in the piston eventually stopping and thus be satisfactory for some purposes, it often involves fairly complicated and expensive pneumatic fluid control mechanisms. Further, there is generally insufficient control over the exact position at which the piston is stopped by this method and doesn't provide for inertial forces of the load. Still further, such a means would permit the piston to drift because of the equal pressure in both chambers and the absence of any positive braking means.
Another means for stopping or braking a specific type of band cylinder is embodied in a device manufactured by Mosier Industries Incorporated of Brookville, Ohio. Such device utilizes an inflatable bladder or other means which expand into braking engagement with the inside surface of a tubular portion of the cylinder. Although this device may be satisfactory for certain applications, it is limited to a particular type of pneumatic cylinder and requires a cylinder member significantly larger than what would normally be required. Thus, it is quite expensive and cumbersome.
Accordingly, there is a real need for an improved pneumatic cylinder having an improved brake mechanism which can be utilized to stop reciprocal movement of the piston when desired.